In-mold coating compositions for optical lenses

ABSTRACT

A composition adapted for use in an in-situ coating process for coating an optical surface for ophthalmic applications. A coating composition according to the present invention includes at least one multifunctional acrylate compound which is cured onto a heated surface with controlled coating distribution in an ophthalmic injection mold. For example, the composition may include an acrylic base cured with an initiator, e.g., t-butyl perbenzoate, and may further include at least one catalyst and at least one metal salt. An acrylic base according to the present invention may include a combination of monofunctional and/or multifunctional acrylate and/or methacrylate compounds.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to coating technology, and inparticular, to a composition adapted for use in an in-situ coatingprocess for coating an optical surface for ophthalmic applications.

2. The Prior Art

In situ coating is a technology that integrates a lens coating processwith a lens injection molding process. More specifically in the lensfield, this technology involves directly injecting coating liquid intothe mold to cover the exterior surface of the substrate lens. Thechallenge in ophthalmic applications is to optimize the coatingchemistry and the molding process to retain the coating properties interms of optical properties, mechanical properties and functionalproperties and to obtain the uniform coating thickness distribution withdesirable thickness.

The prior art is well furnished in the topic of in mold coatingprocesses but is not related and compatible with means characteristicsrequired in the optical field and more specifically in the ophthalmiclens field. The patent application WO 03/031138 described a coatingspecifically formulated for use in an in-mold coating process, but allof these coatings comprised styrene polymer which is not compatible withoptical requirements. Namely, styrene etches the polycarbonate lens andturns it hazy. Also, it is a high risk and hazardous (cancer mutating)agent.

A typical ophthalmic polycarbonate lens is produced by injectionmolding. The lens has to be degated from the injection tree and preparedfor the deposition of an abrasion resistant coating. Usually, abrasionresistance is required due of the soft nature of an injected thermalplastic polycarbonate lens. A completed abrasion resistant coated lenscan take up to at least one day to prepare. In a typical production, theprocess can be weeks.

Also, the typical process of the prior art does not provide any otheradd-on-value for specialty lenses such as anti-reflective, reflective,photochromic, selective light blocking, decorative, multifocal, etc.properties, in addition to abrasion resistance.

It is an object of the present invention to propose a new coatingchemistry specifically adapted to use in the in-situ coating technologyof optical lens, and more particularly of ophthalmic lens based on athermoplastic substrate like polycarbonate.

SUMMARY OF THE INVENTION

The present invention provides a direct and innovative way to coat anophthalmic thermoplastic lens, and more particularly a polycarbonatelens, by combining the coating with the injection molding cycle. Thecoating is optically clear and the coating thickness can range fromabout 1 micron to about 100 microns. Advantageously, a coating accordingto the present invention is compatible with a lens material so as toadhere without causing any undesirable effects.

Also, the present invention will allow a variety of add-on-value in-moldcoatings so as to provide lenses having additional properties, such asphotochromic, anti-reflective, reflective, selected light blocking,decorative, multifocal, etc. properties, preferably in addition toabrasion resistance.

Accordingly, it is an object of the present invention to produce acoating which provides and/or includes at least the followingcharacteristics:

-   -   the coating is solvent free; in fact no volatile organic        compounds (VOCs) should be generated during the in-mold coating        process, which could perturb the polymerization parameters and        thus the optical property of the lens;    -   the coating is cured at a thermoplastic substrate high molding        temperature while maintaining its optical clarity without        etching the thermoplastic substrate;    -   the coating can flow across the front surface of the lens before        it gels and fast cures thereafter; the kinetic parameters are        important to improve flow characteristics;    -   the coating, advantageously, will impart desirable functional        properties onto an ophthalmic lens such as, tintability, scratch        resistance, etc.

Advantageously, the present invention successfully integrates an in-moldcoating process with thermoplastic lens injection molding which itselfinvolves high molding temperature and high melt temperature. Indeed, acoating according to the present invention is thermally curable and isoptically clear and does not show visible interference fringes aftercoating onto a lens. Also, incorporating in-mold coating forthermoplastic lenses is energy saving, as a great amount of additionalenergy is not necessary to finish curing the lenses once they areremoved from the mold.

In summary, the present invention provides an optically transparentcoating that is compatible with the lens material in order to adhere toit without causing any undesirable effects while imparting the desiredfeatures (tint, scratch resistance, etc.) onto the lens material. Acoating according to the present invention advantageously remains inliquid form to flow along a heated mold insert to a uniform thicknessand then polymerizes quickly.

In one embodiment, a coating composition according to the presentinvention comprises an in-mold coating composition comprising amultifunctional acrylate compound which is cured onto a heated surfacewith controlled coating distribution in an ophthalmic injection mold.

In yet another embodiment, a composition for use in in-mold thermallycured coating of ophthalmic lenses is provided comprising at least oneacrylate compound comprising at least a multifunctional acrylate and amonofunctional methacrylate, at least one catalyst and a metal salt.

In yet another embodiment, a coating composition according to thepresent invention comprises a tetra- or hexa-functional urethaneacrylate for hardness and rigidity blended with difunctional acrylatesfor toughness and flexibility. Monofunctional acrylates, preferablymonofunctional methacrylates are included to serve as reactive diluentsand kinetic modifiers to improve flow characteristics. A catalyst orinitiator is incorporated to contribute peroxide (for oxidizing metal),and a metal complex (co-catalyst or accelerator) is added. A surfactantis added to improve the flow of the coating across the mold insert.

These and other aspects, features and advantages of the presentinvention will be described or become apparent from the followingdetailed description of preferred embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A coating composition according to the present invention is preferablysolvent-less, and includes an acrylate compound. The acrylate compoundis preferably thermally cured, which means the coating may be cured via,e.g., azo, peroxides, and/or blocked tertiary amine. Chemicallyspeaking, the coating composition preferably includes multi-functionalacrylates comprising up to hexa functional groups and with variousmolecular weights. Preferably, the present invention comprises amulti-functional urethane acrylic coating that is modified to meetvarious competing requirements. For example, such coating needs to stayin liquid form to flow along a hot mold insert to an even thickness andthen polymerize rather quickly, since the lens molding process is beingextended by the coating set time.

More particularly, a coating composition according to the presentinvention preferably comprises acrylates including monofunctionalacrylates and/or monofunctional methacrylates such as isobornyl acrylateand hydroxylpropyl methacrylate, as well as tetrafunctional acrylatesand/or tetrafunctional methacrylates and hexafunctional acrylates and/orhexafunctional methacrylates. Exemplary acrylates that may be used inthe present invention may include and are not limited to reactivemultifunctional acrylates, preferably hexafunctional aliphatic urethaneacrylates. For example, exemplary acrylates used in the presentinvention may include hexafunctional acrylates and at least onedifunctional acrylate.

As used herein, the term “(meth)acrylate” refers to either thecorresponding acrylate or methacrylate.

Acrylates may be obtained from UCB Chemicals or from Sartomer and Henkel(a German Co.), and may in one embodiment comprise, e.g., Ebecryl™ brandacrylates.

A brief general description of various Ebecryl acrylates in EB numberformats which may be used according to the present invention is asfollows:

-   -   1) 284: aliphatic urethane diacrylate diluted 12% with HDOHA.        Excellent light fastness, exterior durability, toughness and        good flexibility.    -   2) 1290: hexafunctional aliphatic urethane acrylate containing        an acrylated polyol diluent. Provides fast cure with excellent        hardness, solvent and abrasion resistance.    -   3) 5129: hexafunctional aliphatic urethane acrylate combining        good scratch resistance with improved flexibility    -   4) 8301: hexafunctional aliphatic urethane acrylate containing        an acrylated polyol diluent.

Use of hydroxylpropyl methacrylate presents a particular interest toslow down the reaction in the coating composition.

Multi-functional acrylates of three functional groups or higheradvantageously will provide more cross linking and result in higherabrasion resistance. For example, hexa-functional acrylates will providea high degree of cross linking due to having six (6) functional groups.The urethane backbone of these high functional acrylates providesflexibility and greater ability to resist heat. Difunctional acrylatespecies are used to increase the flexibility and toughness and tocontrol the viscosity of the formulation for process-ability to acertain extent.

A monofunctional methacrylate, such as hydroxylpropyl methacrylate,serves as a monofunctional diluent and kinetic modifier. It is used toterminate the reaction or to slow down the propagation of polymerizationso that it will have some stability and a window of reactivity forprocessing. Monofunctional methacrylates used in a composition accordingto the present invention serve as reactive diluents and kineticmodifiers to improve flow characteristics.

With regards to the term acrylates, it is to be noted that methacrylatesand other unsaturated compounds, whether mono- or multifunctional mayalso be used in addition to or instead of acrylates. In some casesmethacrylates may experience a slower chemical reaction duringpolymerization. Acrylate or methacrylate compounds may be selected fromthe family of aliphatic urethane acrylates which include, e.g., from twoto about six functional groups.

A coating formulation having a particular ratio of acrylatederivative(s) (e.g., one example of preferred ratios is shown in Table 1below) advantageously facilitates the provision of a coating compositionwhich is compatible with optical criteria required for ophthalmiclenses.

In a preferred embodiment of the present invention, high molecularweight acrylates (for example, acrylates having a molecular weight of atleast 1000 centipoises (cps) or higher at 25° C.) are preferably usedfor ophthalmic injection molding according to the present invention.This embodiment presents the advantage of improved control of theviscosity and flow of the coating composition on a heated surface. Forexample, a high injection pressure requires a high viscosity flow toallow for the higher temperature (i.e., higher than room temperature)during applied extrusion. It is to be noted that the viscosity mayfurther be adjusted as necessary based on the particular injectionmolding parameters and requirements.

In one embodiment of the present invention, the coating compositionpreferably comprises an acrylic base cured with an initiator (e.g.,t-butyl perbenzoate). In fact, the thermal cure process of the presentinvention utilizes free radical polymerization. The initiator (t-butylperbenzoate) obtains energy by absorbing heat to decompose and generatefree radicals (that is, the free radical reaction is generated bythermal heating). These free radicals then attach monomers or oligomers(reactive multifunctional acrylates) to generate more free radicals topropagate the reaction to form long molecular chains and eventually across-linked network.

An in-mold coating composition according to the present inventionpreferably may further include at least one catalyst (initiator) and atleast one metal salt. The catalyst may be selected from, e.g., alkylaralkyl peracide, azo derivatives and blocked tertiary amine, ispreferably selected from ketone peroxides, diacyl peroxides,dialkylperoxides, diperoxyketals and peroxyesters, and in a verypreferred embodiment comprises tert-butylperbenzoate.

The examples disclosed herein preferably use peroxides derived fromalkyl aralkyl peracide with a metal salt promoter. Peroxides are used tocure the coating via a free radical reaction. Metal salt promoters helpto generate free radicals quickly and minimize oxygen inhibition. Themetal salt and peroxide concentration are preferably chosen to fit acuring cycle for the current process. The concentration ratio can bevaried as necessary to fit a particular process requirement. Again,although use of peroxides for curing is a preferred method, and morespecifically tert-butyl perbenzoate is a preferred candidate,alternative methods for curing may include use of azo and blockedtertiary amine.

The metal salt is preferentially selected from cobalt naphthenate,cobalt octoate, cobalt neodecanoate, copper naphthenate, zincnaphthenate, and potassium octoate, and preferably, the metal saltcomprises cobalt naphthenate.

In one embodiment, an exemplary coating composition according to thepresent invention comprises the following:

-   -   a. at least one hexafunctional acrylate and/or hexafunctional        methacrylate compound;    -   b. at least one difunctional acrylate and/or a difunctional        methacrylate compound;    -   c. Hydroxylpropylmethacrylate;    -   d. Isobornyl acrylate;    -   e. T-butyl perbenzoate; and    -   f. Cobalt naphthenate.

An in-mold coating composition according the invention may optionallyfurther include a surfactant which is preferably selected from afluorinated surfactant or a silicone surfactant.

The coating composition may also optionally include acrylic or epoxyfunctionalized colloids, for example, OG-101 or OG-103 (available fromCLARIANT), or functionalized colloidal silica with acrylic silanes, orother colloids such as, e.g., cerium colloid, niobium colloid, andantimony colloid.

An in-mold coating composition according to the present invention mayfurther optionally include, e.g., a metal alkoxide which may beselected, for example, from zirconium isopropoxydes, methyltrimethoxysilane and tetraethoxysilane.

A coating composition according to the present invention may furtheroptionally include at least one dichroic dye, a photochromic dye and/orone liquid crystal.

It is to be understood by one of ordinary skill in the art that thecoating should preferably retain its qualities at the lens substratemolding temperature. e.g., for a polycarbonate substrate, suchtemperature is around 250° F.

Upon coating of an optical lens, a coating according to the presentinvention is optically clear and may have a thickness ranging from about1 micron to about 100 microns. For example, typical abrasion resistancecoating thickness ranges from about 1 micron to about 8 microns, and aphotochromic system can be up to about 20 microns or more.

Advantageously, an in-mold coating composition according to the presentinvention provides very good anti-abrasion properties. To furtherincrease abrasion resistance, it is also possible to include in thecoating formulation according to the present invention acrylic or epoxyfunctionalized colloids, as discussed above. Metal alkoxides and itsderivatives may also optionally be added as discussed above to increaserefractive index, abrasion resistance and perhaps influence the rate ofpolymerization.

According to one embodiment, a coating composition according to thepresent invention comprises the following: Hexafunctional aliphaticrange: about 33% to 52% preferred: 50% urethane acrylate Aliphaticurethane diacrylate range: about 13% to 31% preferred: 25% diluted 12%with HDOHA Isobornyl acrylate range: about 6% to 9% preferred: 7.6%Hydroxylpropyl methacrylate range: about 12% to 18% preferred: 16%Tetrabutylperoxybenzoate range: about 0.5% to 2% preferred: 1% Metalcomplex range: about 0.25 to 1% preferred: 0.4% (e.g., cobaltnaphthenate)

EXAMPLES

The following Table 1 lists components of an exemplary coatingcomposition according to another embodiment of the present inventionthat was used in exemplary coating processes described in Examples 1, 2and 3 below: TABLE 1 COMPONENT CONCENTRATION (%) Hexa functionalaliphatic urethane acrylate 50.0 Di-functional acrylate 27.0 Hydroxypropylmethacrylate 14.88 Isobornyl Acrylate 7.0 t-butyl perbenzoate 1.0Cobalt Naphthenate 0.1 Surfactant (e.g., EFKA 3034) 0.02Various Exemplary Coating Processes:

Example 1 Post-Injection Coating Process

First, a polycarbonate (PC) lens was injection molded within a mold,having two heated mold inserts. The molding process included a moldtemperature set at 250° F., a melt temperature ranging from 535° F. to565° F., packing pressure set at 450 psi for 12 seconds and a coolingphase of 60 seconds.

At the end of the molding cycle, the mold opened for depositing ofcoating. Without removing the lens from the cavity a thermal curablecoating was deposited in the middle of the injected lens. The mold wasre-clamped and held for 5 minutes at 100° C.

Finally, the mold was opened and the optically clear coated lens wasejected from the mold.

This example typifies a method of coating an ophthalmic lens within amold cavity by first providing an in-mold coating composition which isstable and liquid at room temperature. The coating introduced into themold cavity, either before or after the lens is injected. The coating iscured as an integral component of the lens at the resin solidificationtemperature of the mold cavity.

Example 2 Stamp-Coating process

A metal plate which has a circular recess about 50 μm deep waspositioned horizontally on the parting surface of the mold. A limitedamount of liquid coating was deposited onto the circular recess,referred to as a “cliché”.

An air-inflated silicone membrane, driven by a pneumatic cylinder, moveddownward to pick up the coating from the cliche and then moved back.After the cliche was removed from the mold parting surface, the siliconemembrane then moved downward again to press against the heated moldinsert and held there to let the coating pre-cure for 2 minutes. Afterthat, the silicone membrane was removed with the coating remaining onthe metal insert.

The mold was closed for the PC lens molding. The PC lens moldingconditions were the same as the regular PC molding conditions asdescribed above in example #1. At the end of the molding cycle, the moldopened and the coated lens, which is optically clear, was ejected out ofthe mold.

Example 3 Wafer-Coating Process

A liquid coating drop was deposited on the heated concave metal insertby an auto-dispenser. The temperature of the insert was 250° F.

A 1 mm thick polycarbonate optical wafer which has a front surface basecurve that matches with the concave insert base curve, was placed on topof the coating drop to spread the coating out to cover the entire insertsurface.

The mold was immediately closed for PC lens molding. The PC lens moldingconditions used were the same as described in example #1.

Curing of the coating was established via two minute delay prior to PCinjection after the mold is closed. The two minute delay allows thecoating to pre-cure to the degree that it won't be flushed away from thegate or damaged by the injected PC melt.

At the end of the lens injection molding cycle, the mold was opened andthe coated PC lens, which is optically clear, was ejected out of themold.

Please note, for this method, the PC wafer used to spread out thecoating turns into an integral part of the final coated lens. Itutilizes the advantage of the Engel machine in which the mold opens andcloses vertically. This method may not work on horizontal machines aswell as it does on the vertical Engel machine.

A surfactant such as a fluorinated surfactant (e.g., EFKA 3034) or asilicone surfactant (e.g., Silwet L-7602) may also be included in acoating composition according to the present invention. The surfactantin the coating composition may be added to improve wetability of themold surface.

Exemplary Coating Formulations:

Mold block inserts made of stainless steel and with a polished opticalsurface used to make PC lens in the injection molding machine were usedin this study, along with pre-molded PC lens. The optical mold block setwas heated at 140° C. in a convection oven with a PC lens that issandwiched between the two mold blocks. The optical curvature (basecurve) of the mold block is matching to the lens optical curvature. Theblock was removed from the oven and a coating according to the presentinvention was immediately dispensed on the surface of the mold block.The heated PC lens was immediately pressed onto the dispersed coatingand the mold block set was reassembled and placed back into theconvection oven for 5 minutes at 140° C. to cure the coating.

The coating was cured and transferred onto the PC lens surface with goodadhesion and provided scratch and abrasion resistance to the PCsubstrate.

The following Table 2 lists components of exemplary coating formulationsA, B and C by weight (grams) according to the present invention whichprovided a transparent coating: TABLE 2 Compounds Example A (g) ExampleB (g) Example C (g) Hexafunctional (8301) 13 g (5129) 13 g (588) 13 galiphatic urethane acrylate (e.g., Ebecryl #) Aliphatic urethane 7 7 7diacrylic diluted 12% with HDOHA (e.g., Ebecryl 284) Isobornyl acrylate2 2 2 2-hydroxypropyl 4 4 4 methacrylate Cobalt naphthenate 0.1 0.1 0.1t-Butyl perbenzoate 0.26 0.26 0.26

It is to be noted that in Example B above, the composition may furtherinclude a photochromic dye (e.g., photochromic dye 1077) in the amountof 0.05 grams. The incorporation of such photochromic or cosmetic dyeswould be considered a functional optical additive to the coating. Thecoating also includes a protective hard-coat component, i.e.difunctional or multi-functional (meth)acrylates. The diluent componentconsists of a methacrylate and is combined with a catalyst and a metalsalt.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of ourclaims. Although illustrative embodiments of the present invention havebeen described, it is to be understood that the present invention is notlimited to those precise embodiments, and that various other changes andmodifications may be affected therein by on skilled in the art withoutdeparting from the scope or spirit of the present invention. All suchchanges and modifications are intended to be included within the scopeof the invention as defined by the appended claims.

1. An in-mold coating composition comprising a multifunctional acrylatecompound which is cured onto a heated surface with controlled coatingdistribution in an ophthalmic injection mold.
 2. The coating compositionaccording to claim 1, wherein the coating composition comprises at leastone compound which is selected from a monofunctional (meth)acrylatecompound, a difunctional (meth)acrylate compound and a multifunctional(meth)acrylate compound.
 3. The coating composition according to claim1, wherein the coating composition comprises a mixture of at least two(meth)acrylate compounds.
 4. The coating composition according to claim3, wherein the (meth)acrylate compounds are selected from the family ofaliphatic urethane acrylates which comprise from two to six acrylatefunctionality.
 5. The coating composition according to claim 1, whereinthe acrylate compound comprises at least a hexafunctional (meth)acrylatecompound.
 6. The coating composition according to claim 1, wherein theacrylate compound comprises at least a monofunctional (meth)acrylatecompound.
 7. The coating composition according to claim 1, wherein theacrylate compound comprises at least a mixture of at least onemultifunctional (meth)acrylate, at least one difunctional(meth)acrylate, and at least two monofunctional (meth)acrylates.
 8. Thecoating composition according to claim 1, wherein the acrylate compoundcomprises at least a mixture of at least one hexafunctional(meth)acrylate, at least one difunctional (meth)acrylate, and at leasttwo monofunctional (meth)acrylates.
 9. The coating composition accordingto claim 1, wherein the acrylate compound comprises at least a mixtureof isobornyl acrylate and 2-hydroxy-methacrylate.
 10. The coatingcomposition according to claim 1, wherein the acrylate compound has amolecular weight of at least 1000 cps at 25° C.
 11. The coatingcomposition according to claim 1, further including at least onecatalyst and one metal salt.
 12. The coating composition according toclaim 11, wherein the catalyst is selected from alkyl aralkyl peracide,azo derivatives and blocked tertiary amine.
 13. The coating compositionaccording to claim 11, wherein the catalyst is selected from ketoneperoxides, diacyl peroxides, dialkylperoxides, diperoxyketals andperoxyesters.
 14. The coating composition according to claim 11, whereinthe catalyst comprises tert-butyl-perbenzoate.
 15. The coatingcomposition according to claim 11, wherein the metal salt is selectedfrom cobalt naphthenate, cobalt octoate, cobalt neodecanoate, coppernaphthenate, zinc naphthenate, and potassium octoate.
 16. The coatingcomposition according to claim 11, wherein the metal salt comprisescobalt naphthenate.
 17. The coating composition according to claim 1,wherein the composition comprises at least: a hexafunctional(meth)acrylate compound; a difunctional (meth)acrylate compound;hydroxyl(propyl)methacrylate; isobornyl acrylate; t-butyl perbenzoate;and cobalt naphthenate.
 18. The coating composition according to claim1, wherein the composition comprises: about 20% to 80% of ahexafunctional (meth)acrylate compound; about 10% to 60% of adifunctional (meth)acrylate compound; about 5% to 25% ofhydroxyl(propyl)methacrylate; about 1% to 15% of isobornyl acrylate;about 0.1% to 5% of t-butyl perbenzoate; and about 0.01% to 1% of cobaltnaphthenate.
 19. The coating composition according to claim 1, furtherincluding a surfactant.
 20. The coating composition according to claim19, wherein the surfactant is selected from a fluorinated surfactant anda silicone surfactant.
 21. The coating composition according to claim 1,further including acrylic or epoxy functionalized colloids.
 22. Thecoating composition according to claim 1, further including a metalalkoxyde.
 23. The coating composition according to claim 1, for use asan anti-abrasion coating for ophthalmic lens.
 24. The coatingcomposition according to claim 1, further including at least onephotochromic dye.
 25. The coating composition according to claim 1,further including at least one dichroic dye and one liquid crystal. 26.The coating composition according to claim 1, wherein the compositioncomprises: about 50% of a hexafunctional (meth)acrylate compound; about26% of a difunctional (meth)acrylate compound; about 15.3% ofhydroxyl(propyl)methacrylate; about 7.6%; of isobornyl acrylate; about1% of t-butyl perbenzoate; and about 0.1% of cobalt naphthenate.
 27. Acoated ophthalmic lens including the in-mold applied coating compositionof claim
 1. 28. A method of coating an ophthalmic lens within a moldcavity comprising: providing an in-mold coating composition which isstable and liquid at room temperature; introducing the coating into themold cavity; and curing the coating as an integral component of the lensat the resin solidification temperature of the mold cavity.
 29. Anophthalmic lens coated according to the method of claim 28
 30. Acomposition for use in in-mold thermally cured coating of ophthalmiclenses comprising: a protective hard-coat comprising at least onecompound selected from the group consisting of a difunctional(meth)acrylate, a multifunctional (meth)acrylate, and combinationsthereof; a diluent consisting of a methacrylate; at least one catalyst;and a metal salt.